Dubai: Al Qaeda on Thursday threatened the imminent execution of an American journalist it kidnapped in Yemen, mocking as "foolish" a recently failed bid by US forces to free him.

Al Qaeda in Yemen released a video dated December 2014 naming the hostage as Luke Somers, 33, saying the photojournalist was kidnapped more than a year ago in Sanaa.

US-based monitoring agency SITE Intelligence Group said Somers was seized in the Yemeni capital in September 2013.

Nasser bin Ali Al-Ansi, of Al-Qaeda in the Arabian Peninsula (AQAP), threatened in the video to kill him in three days if Washington fails to meet unspecified demands.

The Yemeni defence ministry said last week Al-Qaeda had moved hostages, including an American journalist, a Briton and a South African, days before a raid in southeastern Hadramawt province to free the American.

Ansi mentioned a "failed operation" in Hadramawt in which militants died, describing it as the "latest foolish action" by the United States.

Yemen had confirmed the operation but made no mention of US forces taking part.

US media reported that American commandos had carried out the raid with Yemeni troops to try to free the US captive.

The New York Times said the commandos found eight other hostages during the raid, including six Yemenis, but not the American.

The Pentagon confirmed Thursday that US and Yemeni forces had tried unsuccessfully recently to rescue Somers.

"Some hostages were rescued, but others -- including Somers -- were not present at the targeted location," spokesman Rear Admiral John Kirby said.

Details of the operation remained classified but the Pentagon decided "to provide accurate information given that it is being widely reported in the public domain," Kirby said.

The Pentagon vowed to work relentlessly to "bring people home whenever we can," he added.

"The United States will not tolerate the abduction of our people, and will work tirelessly to secure the safety of our citizens and to hold their captors accountable."Hundreds of people have been kidnapped in Yemen during the past 15 years, mostly by tribesmen who use them as bargaining chips in disputes with the government.

Nearly all have been freed unharmed.

While AQAP is considered by Washington as the most dangerous affiliate of al Qaeda, it is not known for frequently executing foreign hostages.

Its threat follows the murder of five Western hostages since August by the Islamic State group that controls parts of Syria and Iraq.

Two US journalists, James Foley and Steven Sotloff, American aid worker Peter Kassig, and British aid workers Alan Henning and David Haines were executed.

Yemen is a key US ally in the fight against al Qaeda, allowing Washington to conduct a longstanding drone war against the group on its territory.

The militant group has exploited instability in the impoverished country since a 2011 uprising forced president Ali Abdullah Saleh to step down.

And in recent years there has been a growing number of abductions by al Qaeda, several of whose hostages remain in captivity.

They include a South African teacher and two diplomats, one from Iran and the other from Saudi Arabia.